The present invention is directed to integrated circuits. More particularly, embodiments of the invention provide methods and systems for telecommunication applications. Merely by way of example, embodiments of the invention have been applied to subscriber line control circuits and subscriber linefeed circuits for interfacing with digital equipment in a central office. But it would be recognized that the invention has a much broader range of applicability. For example, embodiments of the invention can be applied in communication networks such as cable television networks, fiber optic, Ethernet port interface to the Internet, VoIP, and wireless local loop, etc.
In a Plain Old Telephone Service (POTS) system, several functions are needed for telephony signaling, subscriber line supervision, and telephone equipment operations. These functions include battery feed, over voltage protection, ringing, supervision, codec, hybrid, and testing, etc. These electronic functions are collectively known by the acronym BORSCHT. BORSCHT circuitry is often found on a telecommunications network line card for implementation of a standard POTS telephone interface for digital equipment in a central office. With the advancement of integrated circuit technology, BORSCHT circuitry can be integrated into a chipset. For example, a line card may include a SLIC, or a subscriber line interface circuit, and a CODEC circuit. In a conventional design, the SLIC typically handles the analog functions and drives the telephone lines and usually include high voltage devices and circuits, whereas the CODEC typically handles digital signal processing and interface functions. Some conventional line cards may include a SLIC integrated circuit and a CODEC integrated circuit. A conventional line card may also include certain discrete components such as switching relays, large capacitors, etc. These conventional techniques have many limitations, some of which are described in more details below.
From the above, it is seen that an improved technique for subscriber line interface circuit is desired.